The primary objective of this proposal is to develop improved technique of deep hypothermia for repair of congenital cardiac defects in small infants. Through advances in extracorporeal perfusion technology and the use of a new halothane diethyl ether azeotrope we hope to establish an improved method of deep hypothermia that will provide more than 90 minutes of safe circulatory arrest. Investigation of this methodology will additionally provide important basic information on the physiology of hypothermia. Current hypothermia technology is directed toward overriding the thermoregulatory process by a combination of anesthetic depression and application of a negative temperature gradient. We also proprose to study the recently discovered enzyme, Indolyl-3-Alkane Alpha Hydroxylase which has been shown to have a direct effect on the thermoregulatory process, as a first step towards an attempt to control the process itself.